1. Field of the Invention
The present disclosure relates generally to wellbore fluids. More specifically, the present disclosure relates to the recovery of drilling and completion fluids.
2. Background Art
When drilling or completing wells in earth formations, various fluids typically are used in the well for a variety of reasons. Common uses for well fluids include: lubrication and cooling of drill bit cutting surfaces while drilling generally or drilling-in (i.e., drilling in a targeted petroliferous formation), transportation of “cuttings” (pieces of formation dislodged by the cutting action of the teeth on a drill bit) to the surface, controlling formation fluid pressure to prevent blowouts, maintaining well stability, suspending solids in the well, minimizing fluid loss into and stabilizing the formation through which the well is being drilled, fracturing the formation in the vicinity of the well, displacing the fluid within the well with another fluid, cleaning the well, testing the well, fluid used for emplacing a packer, abandoning the well or preparing the well for abandonment, and otherwise treating the well or the formation.
Drilling fluids or muds typically include a base fluid (water, diesel or mineral oil, or a synthetic compound), weighting agents (most frequently barium sulfate or barite is used), bentonite clay to help remove cuttings from the well and to form a filter cake on the walls of the hole, lignosulfonates and lignites to keep the mud in a fluid state, and various additives that serve specific functions.
Historically, the drilling industry has used water-based muds (WBMs) because they are inexpensive. The used mud and cuttings from wells drilled with WBMs can be readily disposed of onsite at most onshore locations. WBMs and cuttings can also be discharged from platforms in many U.S. offshore waters, as long as they meet current effluent limitations guidelines, discharge standards, and other permit limits.
Brines (such as, for example, aqueous CaBr2) are commonly used in WBMs because of their wide density range and the fact that brines are typically substantially free of suspended solids. Brines enhance the performance of WBMs by preventing the hydration and migration of swelling clay to reduce formation damage caused by solids or clay swelling or migration. A brine system may be selected to achieve a suitable density for use in a particular well-drilling operation. One advantage of using brines is that for a formation that is found to interact adversely with one type of brine, there is often another type of brine available with which that formation will not interact adversely. Typically, brines are selected from halide salts of mono- or divalent cations, such as sodium, potassium, calcium, and zinc. Chloride-based brines of this type have been used in the petroleum industry for over 50 years and bromide-based brines, for at least 25 years. Formate-based brines, however, have only been widely used in the industry relatively recently (roughly the past ten years).
Cesium formate, which is a particular formate that has been more recently used in drilling and completion fluids, may be used as a solids-free base fluid. Cesium formate is the heaviest of the clear alkali formate fluids, having a specific gravity of 2.3 (density of 19.2 pounds per gallon). Because of this intrinsic high density, the necessity of weighting agents, such as barium sulfate, which can damage tools and the formation, can be eliminated. Other alkali formates, which are of lower density than cesium formate, and that are typically used in drilling and completion fluids include potassium formate and sodium formate. Lower density formates are often be blended with cesium formate to produce a fluid having a specific gravity between 1.0 and 2.3.
Fluids containing cesium formate have been shown to increase production and improve drilling speeds, which can save time and reduce operating costs. Cesium formate has also been shown to be compatible with all major elements of the drilling (BOP, surface equipment, MWD, LWD and mud motors) and completion equipment (metals and elastomers), under conditions of high temperature and pressure. The monovalent nature of cesium formate reduces the likelihood of reservoir formation damage, providing operators with good control and desirable lubricity downhole. Furthermore, alkali formates do not damage the producing formation or downhole metals as their corrosive alternatives (high-density brines) may do. Because it is biodegradable as well as non-corrosive, cesium formate is considered an environmentally safer product than other drilling fluids on the market.
However, despite the desirable performance that results from a well drilled with cesium formate, there are effective limitations on its use. A fluid that includes cesium formate is relatively expensive, so the economics of drilling require that any available cesium formate be reclaimed and recycled. There are, however, limitations on reclamation processes, in terms of both maximum percentages of cesium formate reclaimed and economical feasibility.
Reclamation processes typical of drilling and completion fluids include removal of dissolved contaminants and any solid cuttings or debris or changes to pH or the coloration of the brine. However, complicating the economic feasibility of reclamation of cesium formate brines, drilling and/or completion operations often result in an influx of water into the cesium formate mud or brine and thus a dilution of the water based mud or brine from its desired cesium formate concentration. Thus, because of the additional volume of water present in a recycled drilling fluid, additional amounts of cesium formate must be added to the fluid to return it to the desired cesium formate concentration level in order to maintain the mud's desired properties. While effective, this approach requires the expense of adding additional cesium formate to each reclaimed barrel of fluid and effectively increases the total volume of reclaimed fluid as compared to the volume of fluid initially used in the well.
Alternative processes of reclaiming a fluid to a desired cesium formate levels include attempts to remove the additional volume of water from the fluid. One of these approaches is to heat off/evaporate the excess water from the reclaimed fluid, which may be performed in large cooling towers or in a high shear mixer. While effective, the heating and evaporation of excess water from the reclaimed fluids require a relatively high amount of energy to bring the brines to their desired salt concentration levels. Another approach uses reverse osmosis to separate excess water from the brine. Because reverse osmosis is naturally a slow and labor intensive process, especially as the brine nears saturation levels, reverse osmosis has also been coupled with a high frequency vibration system to decrease the total cycle time for filtration process. While, more effective than simple reverse osmosis, economical limitations still exist.
Accordingly, there exists a need for means to economically reclaim a wellbore fluid to reduce the amount of contaminant water present in the fluid without altering the fluid's desired properties.